The present invention relates to retractable cord assemblies for use with telephones and other electrical or electronic devices.
Cord reels are used to retract and dispense cords for electrical devices such as telephones. To be operable, the cord must conduct electrical signals. Also, in the case of a retractable cord and reel, the cord may be under retractive spring pressure. Through use, including dispensing, retraction, bending and the like, these cords may eventually suffer failure.
Such cords typically compromise several individual conductors wrapped together. As such a cord bends and rotates, one of its conductors may fail. Upon the failure of a single conductor element, the entire cord is failed.
A frequent point of failure is at the point of connection between the retractable cord and the device. In the case of a telephone, for instance, the point where the cord joins the phone is a frequent failure point. As the handset is moved about, the cord at this connection point is bent at sharper angles than the remainder of the cord, and is thus under greater stress and/or strain. Also, as the handset is used, the cord at this point is rotated. These factors or increased wear at the device connection point often lead to premature failure.
Another frequent failure problem arises for applications that require the cord to travel through a conduit. In the case of a telephone on an airline seat, for instance, a retractable cord reel may be located under the seat, while the handset is located in the armrest. In such an example, the cord reel may be located up to several feet from the handset. A conduit is used to guide the retractable cord between the handset and the reel. In some cases, the conduit must be flexible, for example to allow the airline seat or armrest to fold.
Frequent failures occur under such conditions. One cause of failure is friction that develops between the cord and the conduit as the cord is pulled through the conduit. This friction leads to accelerate wear on the cord through heating of the surface and increased stress on the cord. Another cause of failure is through kinking or cracking of the conduit itself; particularly if it is required to move or otherwise flex. Friction between the retractable cord and conduit can cause the outer surface of the cord to fray or otherwise deteriorate. This increases friction between the cord and the conduit, making operation difficult. Further, this friction increases the stress on the cord and connections, likewise leading to a shortened service life. If the cord does not retract fully, as may be caused by excessive friction, the operator may improperly push or force the cord into the conduit, causing cord kinks, which may lead to failure.
An unresolved need therefore exists for an improved cord and cord reel device that offers improved failure free service life.
It is an object of the invention to provide a multi-conductor cord that offers improved resistance to failure.
It is a further object of the invention to provide a device that offers improved resistance to cord failure at the point of connection to a device.
It is a still further object of the invention to provide a cord and conduit that offers reduced friction and improved durability.
The present invention comprises a cable having a central carrier and a conducting element wrapped about the central carrier. The present invention further comprises a grommet for connecting the cable to a device, the grommet having a head and stem, with a passage through the head and stem for passing the cable. The present invention further comprises a cable and conduit assembly, wherein the cable outer surface and the conduit inner surface are treated to minimize friction there between.
The cable of the present invention comprises a central carrier with one or more perimeter conductors wound about it. An outer insulating sheath may cover the carrier and conductors. Prior art cords that have several individual conductors are typically oriented with a central conductor and remaining conductors helically wound about the central conductor perimeter. It has been discovered that in such cords the central conductor is by far the most frequent failure of the conductors. While the exact reason for this is not known, it is believed that since the perimeter outer wrapped conductors wind about the central conductor in a helical fashion, they have a higher tolerance to withstand flex fatigue associated with bending and twisting. Also, as the cord may be bent or twisted, the helically wound perimeter outer conductors are free to slide or otherwise move, while the central conductor is more fixed in place.
In accordance with these beliefs, an improved cable has been developed which comprises a central carrier element and one or more perimeter conductors helically wrapped about the carrier. The central carrier may be comprised of any of a number of materials, chosen for their strength, relative inelasticity, and low cost. Preferred central carriers include cotton or other materials including synthetic fiber cord, such as nylon, Kevlar, or the like. Although perimeter conductors may be present in numbers from one to as many as may be required, it has been discovered that the present invention offers greatest improvement in service life in cords having at least 5 perimeter conductors. A non-conducting insulating sheath may be used to cover the carrier and perimeter conductors.
The present invention further comprises a grommet for improved connection of a cable to a device such as a telephone hand set. The grommet has a rectangular head portion, a stem portion, and a passage through the head and stem for passing a cord. The grommet head is placed in a device housing, with the stem extending out to receive the cable. The grommet may be comprised of any suitable resilient, compressible elastomer. The grommet of the invention satisfies several needs. The connection point between the cable and the device is a frequent location of failure from flex and torsion fatigue as it is a point of acute bending and twisting. The grommet decreases the cable failure rate as its stem lends flex support to the cable passing through it. As the head portion is rectangular, it resists pull through and rotation after being put in place in a device housing. Further, the grommet serves to anchor a braided sheath layer covering the cord conductors. The braided sheath is locked into place after being woven over the grommet.
Preferably, the passage through the grommet is tapered, with a smaller entrance at the stem end and a larger exit at the head end. When the cable is installed, the tapering results in the outside diameter of the distal end to be enlarged in greater degree than the proximal or head end of the stem. The enlarged outside diameter of the stem end helps to lock the grommet in place in a device.
The present invention further comprises a conduit and cable assembly for improved cable service life. Some cord reel applications require a cord reel to be located at a distance from a device (e.g. telephone handset) to be connected to the cord. In such applications, the cable is guided from the reel to the device by a conduit through which the cable passes. In order to improve the service life of the cable and conduit, the present invention comprises a cable with an outer surface and a conduit with an inner surface where the surfaces are designed to minimize friction there between. While the present invention may comprise surfaces of a wide variety of materials and treatments, a preferred cable comprised of a nylon braid in combination with a preferred conduit inner surface comprised of a smooth, hard, metal plating has been found to result in low friction and extended service life. Other materials may potentially be used, including a Teflon lubricant. The conduit inner surface may be comprised of a number of hard, smooth surfaces, including metallic platings such as electroless nickel plating, electrolytic nickel plating, or chrome plating. Generally, it has been discovered that a polymer cable covering in combination with a metallic plate conduit inner surface results in low friction. The conduit should further be chosen on a basis of flexibility so as to resist cracking, kinking, and collapse. Flexible metal conduits are preferred.
The above brief description sets forth rather broadly the more important features of the present disclosure so that the detailed description that follows may be better understood, and so that the present contributions to the art may be better appreciated. There are, of course, additional features of the disclosure that will be described hereinafter which will form the subject matter of the claims appended hereto. In this respect, before explaining the preferred embodiment of the disclosure in detail, it is to be understood that the disclosure is not limited in its application to the details of the construction and the arrangements set forth in the following description or illustrated in the drawings. The present invention is capable of other embodiments and of being practiced and carried out in various ways, as will be appreciated by those skilled in the art. Also, it is to be understood that the phraseology and terminology employed herein are for description and not limitation.
The objects of the invention have been well satisfied. These advantages and others will become more fully apparent from the following detailed description when read in conjunction with the accompanying drawings.